Quantum Cascade Lasers (QCLs) are unipolar semiconductor lasers that utilize optical transitions between confined electronic sub-bands (e.g., conduction or valence bands) of semiconductor hetero structures. Reliable operation of QCLs in the 3-24 μm wavelength range has been achieved although further improvements may be possible. In continuous wave operation at room temperature, QCLs achieve output powers exceeding 1 W and can be designed with broadband gain and with full width at half maximum (FWHM) of at least 300 cm−1, enabling wide wavelength tunability.
QCLs operate in the mid-infrared or terahertz spectral regions giving rise to a wealth of applications. For example, a QCL operating in the mid-infrared region may be used for sensing and analyzing of chemical and biological agents, as many gas- and liquid-phase chemicals have characteristic absorption features in the mid-infrared region. Thus, detectors incorporating QCLs may be used to identify such chemical or biological agents. Some exemplary applications of QCLs in chemical sensing include medical diagnostics, such as breath analysis, pollution monitoring, environmental sensing of the greenhouse gases responsible for global warming, and remote detection of toxic chemicals and explosives.